The above-mentioned pressure signal contains both an information component, e.g. pressure variations representing heart pulses, and a disturbance component, e.g. pressure variation caused by a blood pump. It is a challenging task to extract the information component by removing the disturbance component. For this purpose, existing methods have for instance employed an additional pressure signal which only contains the disturbance component, which may be referred to as a “pump pressure profile”.
One approach has been presented in WO2009/156175, in which the pump pressure profile is either directly subtracted from the pressure signal or used as input to an adaptive filter structure. The pump pressure profile is a predicted time resolved profile of pressure pulses from a dedicated pulse generator (e.g. a blood pump). The predicted profile has been either mathematically deduced or previously recorded under controlled circumstances, i.e. without influence from other sources in order to obtain a clean profile.
The prior art also comprises WO2010/066405, which proposes eliminating a pump disturbance in a pressure signal by subtracting a mathematically modelled pump contribution from the pressure signal. In an alternative approach, when the pump contribution is unknown, WO2010/066405 proposes repeatedly sampling pressure values at a time point when the pump contribution is known to be minimal and estimating an average heart pulse magnitude based on the standard deviation of the sampled pressure values. The latter technique is only able to generate an estimate of the average heart pulse magnitude, and provides neither information on the shape of the heart pulse, nor data on the magnitude or timing of individual heart pulses.
A field in which the present invention is relevant is extracorporeal blood treatment. In extracorporeal blood treatment, blood is taken out of a patient, treated and then reintroduced into the patient by means of an extracorporeal blood flow circuit. Generally, the blood is circulated through the circuit by one or more pumping devices. The circuit is connected to a blood vessel access of the patient, typically via one or more access devices, such as needles or catheters, which are inserted into the blood vessel access. Such extracorporeal blood treatments include hemodialysis, hemodiafiltration, hemofiltration, plasmapheresis, etc. For monitoring and analysing the behaviour of physiological pressure generators such as the heart or respiratory system, e.g. for monitoring a subject's heart pulse rate, blood pressure and also the condition of the blood vessel access (e.g. to identify so-called Venous Needle Dislodgement, VND), it is thus a desire to extract/isolate pressure data originating from such physiological pressure generators. Examples of such monitoring techniques are found in WO97/10013, WO2009/156174 and WO2010/149726.
However, existing solutions often require extensive memory and processing usage for processing the pressure signals, and they may also be unable to provide instantaneous information about the physiological pulses, such as magnitude, shape and timing. Some solutions also require known or predefined pump pressure profiles to filter the pressure signal. These pump pressure profiles may be difficult to obtain, may increase the complexity of implementation, and may generate unreliable results unless care is taken when measuring/calculating the pump pressure profiles.
Corresponding needs and tasks may arise in other fields of technology. Thus, generally speaking, there is a need for an improved technique for processing a time-dependent pressure signal obtained from a pressure sensor in a fluid containing system associated with a first pulse generator and a second pulse generator, in order to monitor a functional state or parameter of the fluid containing system by isolating a signal component originating from the second pulse generator among signal components originating from the first and second pulse generators. Specifically, the fluid containing system may comprise a first sub-system which comprises (or is associated with) the first pulse generator and the pressure sensor, a second sub-system which comprises (or is associated with) the second pulse generator, and a fluid connection between the first and second sub-systems.